(a) Field of the Invention PA1 (b) Description of the Prior Art PA1 MRG, MGR-411, MGR-S, MRG-H, MRP, MRA-L, MRM-42, MRM-53 (manufactured by TOKUSHIMA SEIYU K.K.) PA1 Beckacite 1110, Beckacite 1111, Beckacite F 231, PA1 Beckacite J-811, Beckacite 1120, Beckacite P-720, PA1 Beckacite J-896, (manufactured by DAINIPPON INK AND CHEMICALS INC.) PA1 PRG, PRP, SPR-N, SPR-A, SPR-H (manufactured to TOKUSHIMA SEIYU K.K.) PA1 Beckacite 1100, Beckacite 1123, Beckacite 1126, Beckacite F-171 (manufactured by DAINIPPON INK AND CHEMICALS INC.) PA1 Pentacite P-406, Pentacite P-423 (manufactured by DAINIPPON INK AND CHEMICALS INC.) PA1 RM-1000, RM-1300, RM-4090, RM-4100 (manufactured by TOKUSHIMA SEIYU K.K.) PA1 EG-8000, EG-9000, HG-H, PE, PE-H (manufactured by TOKUSHIMA SEIYU K.K.) PA1 TLR-21, TLR-57 (manufactured by TOKUSHIMA SEIYU K.K.)
The present invention relates to a liquid developer for use in electrophotography, in particular a liquid developer for use in electrophotography which is prepared by dispersing a toner consisting essentially of a pigment of dye and a specific nonaqueous resin dispersion uniformly in a carrier liquid having a highly insulating property and a low dielectric constant.
Conventional liquid developers for use in electrophotography (which may be called liquid developers or developers for short hereinafter) are prepared by dispersing, in a carrier liquid having a high insulating property and a low dielectric constant such as a petroleum type aliphatic hydrocarbon, a toner consisting essentially of carbon black, organic pigment or organic dye and synthetic or natural resins such as acrylic resin, phenolmodified alkyd resin, staybelite resin, rosin, synthetic rubber, etc., and further consisting of a polarity controlling agent such as lecithin, metallic soap, linseed oil, high fatty acid or the like.
In these developers, the resin contained in the toner adheres to the coloring agent (pigment or dye) and the polarity of the toner is maintained distinctly positive or negative and the toner itself exhibits a uniform dispersion stability.
In the developing step, the toner as aforesaid gives rise to electrophoresis depending upon the degree of charge of an electrostatic latent image formed on the surface layer of the electrophotographic photosensitive material (or electrostatic recording material) so as to be fixed on the surface, whereby a copied image is formed. However, the developers were defective in that because the resin and/or the polarity controlling agent constituting the toner diffuse and dissolve in the carrier liquid with the passing of time, the polarity becomes indistinct. When using such developers, accordingly, there are brought about deterioration of image density and fixability, increase in background contamination and so forth, resulting in the copied image being poor in sharpness. In addition, because the printing durability is low and the change of developers with the passing of time is large there can not be obtained images having a high concentration.
Still further, such conventional developers, once the toner agglomerates, were difficult to be re-used, because it was impossible to re-disperse the agglomerated toner in the carrier liquid. Due to these deficiencies inherent thereto, such conventional liquid developers were not suitably used for offset printing or transfer such as charge transfer, press transfer, magnetic transfer and the like.